Refrigerators are low-temperature refrigerating machines that perform sequential thermodynamic cyclic-process (see, for example, U.S. Pat. No. 2,906,101). A one-stage refrigerator includes a chamber having a displacer. The chamber is connected to a high-pressure gas source and to a low-pressure gas source in alternation, so that sequences of a thermodynamic cyclic process (Stirling process, Gifford/McMahon process) occur during the reciprocating motion of the displacer. The consequence is that heat is withdrawn from a specific region of the chamber. For example, temperatures down to below 10 K. can be produced with two-stage refrigerators of this type and with helium as the working gas.
What is referred to as the cold head is that part of a refrigerator that is essentially composed of the actual refrigerator (housing with displacer) and of a gas control system (see German OS 30 44 427). In a known fashion, the gas control system includes a valve system that connects the high-pressure gas source and the low-pressure gas source with the gas channels in a defined sequence. When the refrigerator is fashioned in two stages, two displacers are present that are accommodated in a two-stage cylinder or refrigerator housing. German OS 32 01 496 discloses the possibility of fashioning the gas control system and the refrigerator as separate component parts. This structure is typically known as a split cold head.
The previously known structure of the refrigerator housing is exemplified by German OS 30 44 427. It is composed of a cylinder section that is manufactured of raw material by machining operations (turning, grinding, honing or the like). The cylinder section has the following functions:
formation of the working space;
tight enclosure of the helium gas;
optimally friction-free guidance of the displacer;
track for the seals;
low heat conduction; and
compressive strength up to about 30 bar working pressure.
The material utilized and the processing are involved and expensive in the manufacturing method of the prior art, since precise thin wall tubes having a high interior surface quality must be manufactured. For strength reasons, the wall thickness of the cylinder tubes manufactured using these processes cannot fall below 1 mm, this simultaneously meaning that the heat conduction along the cylinder tube cannot fall below a defined degree. The level of heat conduction inherent in these processes deteriorates the efficiency of the refrigerator, since heat is constantly supplied to the cold end of the cylinder via the cylinder housing itself.